The nitrogen-fixing rhizobia-legume symbiosis relies on a complex interchange of molecular signals between the two partners during the whole interaction. On the bacterial side, different surface polysaccharides, such as lipopolysaccharide (LPS) and exopolysaccharide (EPS), might play important roles for the success of the interaction. In a previous work we studied two Sinorhizobium fredii HH103 mutants affected in the rkpK and lpsL genes, which are responsible for the production of glucuronic acid and galacturonic acid, respectively. Both mutants produced an altered LPS, and the rkpK mutant, in addition, lacked EPS. These mutants were differently affected in symbiosis with Glycine max and Vigna unguiculata, with the lpsL mutant showing a stronger impairment than the rkpK mutant. In the present work we have further investigated the LPS structure and the symbiotic abilities of the HH103 lpsL and rkpK mutants. We demonstrate that both strains produce the same LPS, with a truncated core oligosaccharide devoid of uronic acids. We show that the symbiotic performance of the lpsL mutant with Macroptilium atropurpureum and Glycyrrhiza uralensis is worse than that of the rkpK mutant. Introduction of an exoA mutation (which avoids EPS production) in HH103 lpsL improved its symbiotic performance with G. max, M. atropurpureum, and G. uralensis to the level exhibited by HH103 rkpK, suggesting that the presence of EPS might hide the truncated LPS produced by the former mutant.

中文翻译：

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胞外多糖不利于具有截短脂多糖核心的 Sinorhizobium fredii HH103 突变体的共生性能。


固氮根瘤菌-豆科植物共生关系依赖于整个相互作用过程中两个伙伴之间分子信号的复杂交换。在细菌方面，不同的表面多糖，如脂多糖 （LPS） 和胞外多糖 （EPS），可能对相互作用的成功起重要作用。在之前的工作中，我们研究了两个受 rkpK 和 lpsL 基因影响的 Sinorhizobium fredii HH103 突变体，它们分别负责葡萄糖醛酸和半乳糖醛酸的产生。两个突变体都产生了改变的 LPS，此外，rkpK 突变体缺乏 EPS。这些突变体与 Glycine max 和 Vigna unguiculata 的共生关系受到不同的影响，其中 lpsL 突变体表现出比 rkpK 突变体更强的损伤。在本工作中，我们进一步研究了 HH103 lpsL 和 rkpK 突变体的 LPS 结构和共生能力。我们证明两种菌株产生相同的 LPS，具有不含糖醛酸的截短核心寡糖。我们表明 lpsL 突变体与 Macroptilium atropurpureum 和 Glycyrrhiza uralensis 的共生性能比 rkpK 突变体差。在 HH103 lpsL 中引入 exoA 突变（避免 EPS 产生）将其与 G. max、M. atropurpureum 和 G. uralensis 的共生性能提高到 HH103 rkpK 表现出的水平，表明 EPS 的存在可能隐藏了前一个突变体产生的截短 LPS。